Emulsions are water- or oil-based solutions, in which the compounds are present in dissolved form, that are characterized as amphiphilic due to their structural properties, thus, enabling hydrophilic and hydrophobic interactions. Therefore, the emulsifying effect of such compounds in a liquid system is enhanced by providing optimal interaction between both the water molecules and the organic compounds. Methods and procedures are known from the prior art with which it is possible to prepare emulsions by mixing a water phase and an oil phase. Such emulsions will separate into an oil and water phase spontaneously if amphiphilic compounds are not present. Organic compounds that provide stabilization of water-oil mixtures in the form of an emulsion, in which they are present either as water droplets in oil or oil droplets in water, are called emulsifiers. Emulsions which are stabilized by emulsifiers are suitable for receiving further organic compounds, wherein they align at the phase boundaries according to thermodynamic principles. Therefore, emulsions are very well suited to split non-covalent bindings between organic and inorganic compounds and transfer organic compounds into the liquid emulsion phase. An emulsifier-stabilized emulsion leads to an improvement of the solution properties. In order to achieve a further improvement of dissolution characteristics, the phase boundary must be increased. Insofar solvation systems have been developed that are based on the formation of micro- and nano-emulsions, which exhibit an increased capacity to dissolve organic compounds due to a reduction of the surface tension of such emulsions. Because of the improved solubility of organic compounds that are stabilized by a solvation layer, those organic compounds do not or only to a very small extent aggregate or interact with other compounds that are dissolved. In such a way, dissolved organic compounds remain in a dissolved state for an indefinite duration, even in a predominantly water- or oil-based medium, in which they would not be soluble or dissolve poorly otherwise. The greater solvation potency of such amphiphilic emulsifiers, on the other hand, makes it more difficult to remove the dissolved organic compounds.
WO 2011/160857 A2 discloses methods and procedures to produce nano-emulsions which are suitable to dissolve a variety of organic compounds. In one aspect nano-emulsions are obtained by aqueous solutions of hydrophilic compounds with guanidino and/or amidino groups, which have a Kow<6.3. Kow is referred to the partition coefficient and represents the relation of distribution of a substance between n-octanol and water. It is stated that carboxylic acids electrostatically adhere to guanidino or amidino groups up to an equimolar ratio and that thereby the hydrophobic carboxylic acids obtain a hydration shell, which makes them soluble in an aqueous medium. The electrostatic interaction can be terminated again by protonation of the carboxylic groups of the carboxylic acid. It was found that it is possible to use a solution of dissolved compounds carrying guanidino and/or amidino groups for separation of carboxylic acids from a lipophilic medium with a high separation efficiency.
The dimer that is produced by the interaction of the hydrophilic compounds carrying guanidino and/or amidino groups with carboxylic acids creates a hydration shell, which allows solubilization of this dimer in an aqueous medium and formation of nano-emulsions. In addition, compounds carrying guanidino and/or amidino groups cause detachment of other organic and inorganic compounds that interact with the carboxylic acid. Furthermore, the hydration shell of compounds carrying guanidino and/or amidino groups, on the one hand, and hydrophobic groups of the carboxylic acids, on the other hand, enable electrostatic interactions with complexed organic compounds, whereby they are partially hydrated. A high penetration efficacy of nano-emulsions into densely packed and also anhydrous mixtures of organic matter has already been described in the scientific literature. Nano-emulsions can also be used to separate compounds from the organic complexes in order to retrieve them.
It was shown that solutions of compounds carrying guanidino and/or amidino groups can be used to refine lipid phases. By doing so, concentrations of free carboxylic acids in the lipid phase can by lowered to the minimum values that are required to comply with industrial standards.
Furthermore, other organic compounds that are present in the lipid phases are solubilized and transferred into the aqueous phase forming an aqueous emulsion that can be separated by phase separation.
Those organic compounds can be, in particular, phospholipids, glycolipids but also colouring and flavouring agents. Furthermore, inorganic compounds, such as sodium, potassium, calcium, magnesium, copper, iron, and other compounds are simultaneously removed with the water phase. In addition, advantageous applications were also documented for purification methods and decomplexing methods. This is especially true for materials (e.g., press cake of plants, sewage sludge, fruit skins, or shells) having a relevant content of organic and/or lipophilic compounds, in which it is possible to achieve a high separation efficiency of those organic compounds that are complexed with lipids or inorganic compounds, by the use of solutions of compounds carrying guanidino and/or amidino groups or nano-emulsions consisting of solutions of compounds carrying guanidino and/or amidino groups and carboxylic acids. The enormous emulsion performance of nano-emulsions, consisting of dissolved compounds carrying guanidino and/or amidino groups and carboxylic acids, also leads to an extremely stable solubilization of lipophilic, hydrophilic, and amphiphilic compounds, so that separation of the solubilized organic compounds from such aqueous solutions/emulsions by means of centrifugation (e.g., by ultracentrifugation) is virtually impossible and can only be achieved under drastic conditions, such as a pH shift in a strongly acidic range (e.g., pH<3 [acidic work up]). Such emulsions, which have been cleared from any filterable solids, showed no visible changes over months, in particular, settling of solid components did not occur, provided that larger aggregates have previously been separated. Therefore, the special stability of an emulsion having a mixture of organic compounds prepared in such a manner becomes apparent. Thermal treatment of those emulsions had no effect; extraction tests with solvents, such as hexane, diethyl ether, dimethylformamide or chloroform, showed only a low separation performance for the dissolved organic compounds or the solvents remain partially or completely in the aqueous phase. Adsorptive techniques, such as chromatography, had virtually no separation effects.
A strong protonation of nano-emulsions, consisting of dissolved compounds carrying guanidino and/or amidino groups and carboxylic acids, liberates the carboxylic acids which can then be separated from the aqueous solution by phase separation. For the re-use of solutions containing compounds carrying guanidino and/or amidino groups for the solubilization and separation of carboxylic acids in a lipid phase, however, a pH>7.0 is required in order to achieve a sufficient dissolution capacity for carboxylic acids. Therefore, an acidic workup of said nano-emulsion would necessitate subsequent adjustment of the pH of the solution containing compounds carrying guanidino and/or amidino-groups by means of a base for a further recycling method, and thus the recycling method of the solution containing the compound carrying a guanidino or amidino group would be uneconomical. In addition, chemical reactions of dissolved organic compounds can occur under acidic conditions, leading to unwanted changes. Thus, the organic compounds that are obtained after an acidic workup can usually not be commercially used.
Another known method is based on displacement extraction of the carboxylic acids with an alcohol. It has been shown that lowering of the pH is also necessary here in order to allow a sufficient separation of nano-emulsified fatty acids. The additional presence of an alcohol in an acidic reaction mixture leads to chemical changes of many organic compounds. It was shown that such a method is not appropriate, if the solution containing guanidino- or amidino group carrying compounds should be reused for a renewed separation of carboxylic acids from a lipid phase compounds carrying, since the presence of an alcohol which has remained in the aqueous phase reduces the efficacy of those compounds to separate carboxylic acids. Thus, no methods or techniques are available or are known from the prior art with which the carboxylic acids and/or other organic compounds in nano-emulsions, consisting of compounds carrying guanidino- and/or amidino groups carrying compounds and dissolved carboxylic acids, can be separated under mild conditions as well as with simple and economic measures in order to retrieve the organic compounds and to purify the aqueous solution, so that it is applicable for reuse. In order to meet these requirement, an appropriate method and process technology and apparatus is mandatory, in particular for the processing of nano-emulsions, consisting of compounds carrying guanidino and/or amidino groups and carboxylic acids. Furthermore, it would be particularly advantageous to receive chemically and structurally unaltered organic compounds with high economic value.